Conventional MEMs mirrors for use in optical switches, such as the one disclosed in U.S. Pat. No. 6,535,319 issued Mar. 18, 2003 to Buzzetta et al, redirect beams of light to one of a plurality of output ports, and include an electrostatically controlled mirror pivotable about a single axis. Tilting MEMs mirrors, such as the ones disclosed in U.S. Pat. Nos. 6,491,404 issued Dec. 10, 2002 in the name of Edward Hill, and 6,677,695 issued Jan. 13, 2004 in the name of Dhuler et al, which are incorporated herein by reference, comprise a mirror pivotable about a central longitudinal axis. The MEMs mirror device 101, disclosed in the aforementioned Hill patent, is illustrated in FIG. 1, and includes a rectangular planar surface 102 pivotally mounted by torsional hinges 104 and 105 to anchor posts 107 and 108, respectively, above a substrate 109. The torsional hinges may take the form of serpentine hinges, which are disclosed in U.S. Pat. No. 6,327,855 issued Dec. 11, 2001 in the name of Hill et al, and in United States Patent Publication No. 2002/0126455 published Sep. 12, 2002 in the name of Robert Wood, which are incorporated herein by reference. In order to position conventional MEMs mirror devices in close proximity, i.e. with a high fill factor (fill factor=width/pitch), they must be positioned with their axes of rotation parallel to each other. Unfortunately, this mirror construction restraint greatly restricts other design choices that have to be made in building the overall switch.
When using a conventional MEMs arrangement, the mirror 101 positioned on the planar surface 102 can be rotated through positive and negative angles, e.g. ±2°, by attracting one side 110a or the other side 110b of the planar surface 102 towards the substrate 109. Unfortunately, when the device is switched between ports at the extremes of the devices rotational path, the intermediate ports receive light for fractions of a millisecond as the mirror 1 sweeps the optical beam past these ports, thereby causing undesirable optical transient or dynamic cross-talk.
Articulated MEMs devices, such as those disclosed in U.S. Pat. Nos. 6,495,893 issued Dec. 17, 2002 to Lin et al; 6,760,144 issued Jul. 6, 2004 to Hill et al; and 6,822,370 issued Nov. 23, 2004 to Clark et al, can provide high fill factors, and magnified angular ranges, but do not solve the problem of dynamic cross-talk because of laterally extending fixed hinges, which prevent rotation about two axes. Another advantage of articulated MEMs devices is the separation of actuating electrodes from the mirrored platforms.
One solution to the problem of dynamic cross-talk is to initially or simultaneously rotate the mirror about a second axis, thereby avoiding the intermediate ports. An example of a MEMs mirror device pivotable about two axes is illustrated in FIG. 2, and includes a mirror platform 111 pivotally mounted by a first pair of torsion springs 112 and 113 to an external gimbal ring 114, which is in turn pivotally mounted to a substrate 116 by a second pair of torsion springs 117 and 118. Examples of external gimbal devices are disclosed in U.S. Pat. Nos. 6,529,652 issued Mar. 4, 2003 to Brenner, and 6,454,421 issued Sep. 24, 2002 to Yu et al. Unfortunately, an external gimbal ring greatly limits the number of mirrors that can be arranged in a given area and the relative proximity thereof, i.e. the fill factor. Moreover, the external gimbal ring may cause unwanted reflections from light reflecting off the support frame 113, 114.
Another proposed solution to the problem uses high fill factor mirrors, such as the ones disclosed in U.S. Pat. No. 6,533,947 issued Mar. 18, 2003 to Nasiri et al, which include hinges hidden beneath the mirror platform. Unfortunately, these types of mirror devices require costly multi-step fabrication processes, which increase costs and result in low yields.
Yet another solution to overcome the shortcomings of the prior art is disclosed in U.S. Pat. No. 6,934,439 issued Aug. 23, 2005 to Mala et al (incorporated herein by reference), which provides a high fill factor MEMs mirror device that pivots about the same axis as an adjacent mirror and includes an internal gimbal ring for rotating about perpendicular axes.
An object of the present invention is to overcome the shortcomings of the prior art by providing a MEMs device providing an articulated MEMs device with a high fill factor and extended tilt range, which is tiltable about perpendicular axes.